WASHINGTON — Senate Republicans voted Tuesday to advance to floor debate on their efforts to repeal and replace Obamacare, a hard-fought win for President Donald Trump. Their next challenge is agreeing on a bill.

Vice President Mike Pence cast the tiebreaking vote.

In a dramatic moment, Sen. John McCain returned from Arizona to applause from fellow senators. He cast a necessary Republican vote for the motion.

As the vote began, protesters in the Senate gallery shouted "kill the bill" and "shame, shame, shame!"

Tuesday afternoon's vote will determine if the Senate can start floor debate on legislation to overhaul the Affordable Care Act even though there aren't any guarantees the votes are there to eventually pass it — and it's unclear what a final bill will look like.

President Trump called the Senate passage of the motion to proceed on health care "a big step."

He said at the start of a Rose Garden joint news conference, "I'm very happy to announce that with zero of the Democrats' votes, the motion to proceed on healthcare has moved past and now we move forward toward truly great health care for the American people. We look forward to that. This was a big step."

He added, "I want to thank Sen. John McCain. A very brave man. He made a tough trip to get here."

In a written statement released at the same time, the President said, "I applaud the Senate for taking a giant step to end the Obamacare nightmare.

"As this vote shows, inaction is not an option, and now the legislative process can move forward as intended to produce a bill that lowers costs and increases options for all Americans. The Senate must now pass a bill and get it to my desk so we can finally end the Obamacare disaster once and for all."